Mutagenic compounds occur in the feces of industrial populations known to be at a relatively high level of risk for colon cancer. We are trying to answer the following questions about these compounds. 1. How many types of mutagens are produced? 2. Why do only about 20% of North Americans excrete them? 3. Are they produced or activated by colonic bacteria? 4. Are any of these compounds sensitive to oxygen? To answer the last question we need to develop a totally anaerobic Ames Test. Other work has involved identifying people that excrete mutagens and examining their diet and fecal flora.